An important task of vehicle dynamic control systems and motor vehicle safety systems is to stabilize the vehicle in critical situations, for instance, when it is skidding. The first systems introduced as a standard for solving this task were anti-lock braking systems (ABS) and anti-slip regulation (ASR), also known commonly as traction control systems (TCS), which act primarily on the longitudinal dynamic behavior of the motor vehicle. As a fundamental expansion, vehicle dynamic control systems were developed that influence the behavior of the vehicle to stabilize it also in lateral dynamically critical situations through controlled measures such as active braking of individual wheels, controlling driving torque for implementing slipping at the wheels, and/or through active steering. Such systems are, for instance, the Electronic Stability Program (ESP) or the Active Front Steering (AFS) for controlled steering intervention from BMW.
All vehicle dynamic control systems must initially determine the driving state of the vehicle as precisely as possible, for which motion sensors, among others, are required. The more motion variables and driving state parameters are known, the better and more reliably the driving state can be fundamentally calculated, and the more effectively and safely undesired vehicle behavior can be counteracted. For example, the plausibility of a calculated driving state can be checked with additionally known motion variables. Furthermore, in extraordinary driving situations, for instance extremely steep curves, it may no longer be possible to ensure control and with it stabilization of the vehicle without using such further motion variables. For this however, as a rule further motion sensors are necessary which drive up the costs of a vehicle dynamic control system or safety system. This is the reason for a fundamental endeavor of the manufacturers of such systems to keep the number of necessary sensor elements as low as possible, especially as it is necessary to design these partly redundant for safety reasons, at least for the most important motion sensors, so that for measuring each additional motion variable two sensor elements must be included at correspondingly increased costs.
It is known to determine the driving state based on models, such as observers, for instance tire models, etc. DE 10 2007 047 337 A1 for example, discloses a device and a method in which the transverse velocity of the vehicle is calculated from the measurement of the transverse acceleration using a tire model. The accuracy of the calculation of transverse velocity can be further improved by adding correction variables, for instance the vehicle longitudinal velocity and the yaw rate.
It is further known to determine the direct absolute velocity of the vehicle using a GPS measurement system, as is disclosed DE 101 48 667 C2, for example. The GPS signal, and hence values calculated from the GPS signal, such as the absolute velocity of the vehicle are subject to a certain time delay, and consequently are not well suited for vehicle dynamic control systems, which require driving state information every 5 to 25 ms. Accurate and fast GPS systems, which for example use multiple antennas are not only expensive, but nonetheless still comprise a certain time delay. With multiple antennas it is possible to determine the orientation of the vehicle. However, this means a higher expenditure.
Starting from this background, the object of the present invention is to provide devices and methods that permit optimizing the determination of the driving state of the vehicle, particularly with respect to accuracy, safety, dynamics and costs.